Blank was the architect of the mega-deal that saw Lloyds take over the collapsing HBOS last September. At the time, he called it a "unique opportunity". Lloyds had weathered the credit crunch in pretty good shape up to that point, but now huge losses at HBOS are dragging it down.

Did Blank know about the HBOS losses at the time of the deal?

The Lloyds team knew it was taking on a fragile bank but because of the need to rush through the acquisition, there was little time for traditional due diligence. HBOS's losses have since proved worse than expected.

Why are the losses at HBOS so big?

The bank made a lot of loans to commercial property businesses at the height of the property boom. Many of these are now turning sour and HBOS's business has deteriorated rapidly in the past six months – and there is little sign of any improvement on the horizon.

Why was Gordon Brown involved?

Brown had to waive competition rules to sanction the merger of two high-street banks. Blank's departure is likely to put more pressure on the prime minister.

What has triggered the announcement about Blank's departure?

About a fifth of Lloyds' shareholders were considering a vote against his re-election at the bank's annual meeting in Glasgow next month. It also looks as if UKFI, which holds the taxpayers' stakes in the nationalised banks, would also have voted against him. So he jumped before he was pushed.

When will Blank actually leave?

The bank has said he will step down ahead of next year's annual meeting, which gives time for an orderly succession plan to be put in place.

Who will replace him?

His job is one of the most important in British banking and requires a heavy-hitter. Speculation has centred round Mervyn Davies, former chairman of Standard Chartered bank, who is now the trade minister in the Lords. Davies is one of the few bankers to emerge from the credit crunch with his reputation intact.

Are HBOS's losses under control?

Thebank is trying to staunch the flow of bad debts but will still be hit by a falling property market. It is also a crucial time for Lloyds as it is trying to finalise the details of insuring £260bn worth of assets under the government's asset protection scheme.